Over the past few years, there has been a marked increase in the prevalence of related painful diseases of the feet of dairy cattle called papillomatous digital dermatitis (PDD), digital dermatitis (DD) or interdigital dermatitis (IDD), hereinafter referred to as PDD. Commonly known as footwarts, PDD has been reported in the USA, Canada, Europe, the Mediterranean, Japan, South Africa, Australia, and South America. This disease adversely affects the dairy industry economically through increased treatment costs and by its negative effect on milk production and reproductive performance. It appears as a contagious disease, with some herds having a 90% prevalence of clinical disease.
PDD causes severe lameness, decrease in body condition, and decreased reproductive performance in cattle. First calf heifers are most often affected. Little or no digital swelling occurs. The lesions are limited to the feet, usually the hind feet. Typically, lesions occur at the back of foot near the interditigal ridge. Lesions may range from small, dime-sized, flat, red and circumscribed lesions (early lesions) to large, raised, golf-ball sized, with long brown/black papillary fronds (mature lesions). The long (true) hairs at edge of lesion are frequently hypertrophied. The lesions may persist for many months or may regress in dry weather.
Various attempts to demonstrate viruses, structural group antigens of papillomavirus, and bovine papillomavirus types 1-6 in PDD have been negative (Basset et al., Vet. Rec. 126:164-165 (1990); Read et al., Vet. Rec. 130:59-60 (1992); Read et al., Proc. Amer. Ass. Vet. Lab. Diag. 38:68 (1995); Rebhun, et al., J. Am. Vet. Med. Assoc. 177:437-440 (1980); Scavia et al., Proc. Int. Sym. Dis. Rum. Digit 8:174-176 (1994); Zemljic, Proc. Int. Sym. Rum. Digit 8:164-167 (1994)). Histologic examination for Dermatophilus spp., fungi, and parasites also have been negative (Read et al., Proc. Amer. Ass. Vet. Lab. Diag. 38:68 (1995)).
Because the disease responds to topical or parenteral treatment with antibiotics, a bacterial role in the disease process has been indicated. Spirochetes have been demonstrated invading into the stratum spinosum and dermal papillae of PDD lesions and are the predominant bacterial morphotype present. Spirochetes with morphologic, phenotypic, and genetic characteristics of the genus Treponema have been isolated from PDD lesions (Walker et al., Vet. Micro. 47:343-355 (1995); Walker et al., AJVR 58:744-748 (1997)). Intralesional invasive spirochetes have also been demonstrated in PDD worldwide (Blowey et al., Vet. Rec. 135, 115-117 (1994); Scavia et al., Proc. Int. Sym. Dis. Rum. Digit 8:174-176 (1994); Zemljic, Proc. Int. Sym. Rum. Digit 8:164-167 (1994); Kimura et al., J. Vet. Med. Jpn. 46:899-906 (1993); Dopfer et al., Vet. Rec. 140:620-623 (1997); Choi et al., Int. J. Syst. Bact. 47:175-181 (1997); Rijpkema et al., Vet. Rec. 140:257-259 (1997)).
It remains unclear whether these spirochete organisms have a primary role in lesion development or whether they act as secondary opportunists after the initial PDD lesion has developed. For example, other bacteria such as Serpens spp., a gram negative rod related to members of the genus Pseudomonas, have also been suggested as a PDD agent. In the field, PDD appears contagious but most previous attempts to transmit PDD experimentally have not been successful (Weaver, Proc. 7th Biann. Int. Sym. Dis. Rum. Digit, Copenhagen (1992); Basset et al., Vet. Rec. 126:164-165 (1990); but see Read & Walker, Vet. Pathology 33:607 (1996)).
Currently, the etiologic agent of PDD is unknown. In addition, it is unknown whether PDD can spread to other species, although similar histopathologic lesions have been observed in sheep, horses, and goats. There is therefore a need to definitively identify the etiologic agent for PDD and to develop a means of preventing this disease by developing a vaccine against PDD.